1. Field of the Invention
The present invention relates to an optical transmission device comprising a plurality of nodes connected to each other to form a ring structure. In particular, the present invention relates to an optical transmission device having a ring structure using wavelength division multiplexing technology (WDM).
2. Description of the Related Art
A conventional optical transmission device comprising a plurality of nodes connected to each other to form a ring structure is described as the conventional art with reference to FIG. 16. FIG. 16 is a block diagram for illustrating an exemplary structure of an optical transmission device having a ring structure comprising m nodes, the respective nodes performs optical wavelength division multiplexing of wavelengths 1 to n to transmit optical signals.
In FIG. 16, 901-1 to 901-m represent optical insertion division nodes, 902-1 to 902-4 represent transmission line optical fibers (902-1: counter-clockwise working (or primary) operation system, 902-2: clockwise working operation system, 902-3: counter-clockwise stand-by (or spare) system, and 902-4: clockwise stand-by system, 951 represents an optical pre-amplifier (pre-optical amplifier), 952 represents a wavelength division section, 953 represents wavelength multiplexing section, 954 represents an optical booster amplifier (booster optical amplifier), 955 represents an optical pre-amplifier, 956 represents a wavelength division section, 957 represents a wavelength multiplexing section, 958 represents an optical booster amplifier, 959 represents an optical pre-amplifier, 960 represents a wavelength division section, 961 represents a wavelength multiplexing section, 962 represents an optical booster amplifier, 963 represents an optical amplifier, 964 represents a wavelength division section, 965 represents a wavelength multiplexing section, 966 represents an optical booster amplifier, 967-1 to 967-n represent insertion division (ADM) devices, 971 to 974 represent high speed signal reception interface sections, 975 to 978 represent high speed signal transmission interface sections, 979 represents a cross connector section, and 980 represents a low speed signal interface section.
In FIG. 16, m nodes are connected to form a ring with a total of four transmission line optical fibers, where two of the lines comprise a bi-directional working (or primary) operation system, and where the other two of the lines comprise a bi-directional stand-by (or backup) operation system. Each node transmits a wavelength division multiplexed (WDM) optical signal having n wavelengths of .lambda.1 to .lambda.n to the above-mentioned four optical fiber transmission lines respectively, and each node receives the wavelength division multiplexed optical signal having n wavelengths of .lambda.1 to .lambda.n from the above-mentioned four optical fiber transmission lines.
Next, an operation performed in each node of the conventional optical transmission device having a ring structure as described above is described herein under.
The optical signal received from the counter-clockwise operation system is amplified by the optical pre-amplifier 951, and divided into n wavelength components having wavelengths of .lambda.1 to .lambda.n in the wavelength division section 952. The wavelength-divided n optical signals having wavelengths of .lambda.1 to .lambda.n are inputted to ADM devices 967-1 to 967-n respectively. In detail, the optical signal having a wavelength of .lambda.1 is inputted to the ADM device 967-1, the optical signal having a wavelength of .lambda.2 is inputted to the ADM device 967-2, and the optical signal having a wavelength .lambda.n is inputted to the ADM device 967-n.
n optical signals having wavelengths of .lambda.1 to .lambda.n are outputted from the respective ADM devices 967-1 to 967-n. In detail, the optical signal having a wavelength of .lambda.1 is outputted from the ADM device 967-1, the optical signal having a wavelength of .lambda.2 is outputted from the ADM device 967-2, and the optical signal having a wavelength .lambda.n is outputted from the ADM device 967-n. n optical signals having wavelengths of .lambda.1 to .lambda.n are subjected to wavelength division multiplexing operation in the wavelength multiplexing section 953 to form a single optical signal. The single optical signal is amplified by the optical booster amplifier 954, and then sent out to the counter-clockwise operation optical fiber transmission line. The optical signal that is transmitted/received through other transmission lines, namely, the clockwise working operation system 902-2, counter-clockwise stand-by system 902-3, and clockwise stand-by system 902-4, is subjected to a multiplexing division (or separation) operation involving wavelengths of .lambda.1 to .lambda.n like the above-mentioned operation.
In FIG. 16, the optical pre-amplifier 955, wavelength division section 956, wavelength multiplexing section 957, and optical booster amplifier 958 are applied to the clockwise working operation system, the optical pre-amplifier 959, wavelength division section 960, wavelength multiplexing section 961, and optical booster amplifier 962 are applied to the counter-clockwise stand-by system, and the optical pre-amplifier 963, wavelength division section 964, wavelength multiplexing section 965, and optical booster amplifier 966 are applied to the clockwise stand-by system.
Operation in the ADM device 967-1 is described herein under.
Four optical signals having wavelength of .lambda.1 inputted from the wavelength division sections 952, 956, 960, and 964 are respectively subjected to optical/electric conversion, overhead signal termination, and time-division separation in high speed signal reception interface sections (HSRx) 971 to 974. Afterwards, the optical signals are inputted to the cross connector section 979 as electric data signals. Electric signals are inputted from the cross connector section 979 to the high speed signal transmission interface sections (HSTx) 975 to 978, where the electric signals are subjected to time-division multiplexing, overhead signal insertion, and electric/optical conversion operation, and then optical signals having wavelength of .lambda.1 are outputted to the wavelength multiplexing section 953, 957, 961, and 965. The cross connector section 979 functions to connect four pairs of electric data signals inputted from the high speed reception interface sections (HSRx) 971 to 974 selectively to four pairs of electric signals to be outputted to the high speed signal transmission interface sections 975 to 978 depending on the failure condition of transmission lines in the ring network, and functions to division-connect partially or entirely the input electric data signal to the low speed signal interface section 980 and to insert the signal from the low speed signal interface section 980 in an output data signal.
Next, recovery operation performed when the transmission line of the conventional ring optical transmission device shown in FIG. 16 experiences a failure is described. FIG. 17 is a set of diagrams for illustrating the recovery operation.
In FIG. 17(a) during working (or normal) operation, data signals are communicated through the two operation transmission lines between the node 2 and node 5. In node 2 and node 5, the data signal is inputted from/outputted to the low speed signal interface section in each node, and the cross connector section sets the path.
Recovery operation performed when two operation transmission lines experiences a failure between the node 2 and node 3 is shown in FIG. 17(b). In this case, in the node 2, the cross connector section changes connection from the path that a data signal is allowed to be communicated through the operation transmission line side between the node 3 and node 2 for insertion division, to the path that a data signal is allowed to be communicated to the stand-by transmission line side between the node 3 and node 2 for insertion division. On the other hand, in the node 3, the cross connector section performs path change so that an optical signal inputted/outputted through the node 2 side stand-by transmission line is connected to an optical signal inputted/outputted through the node 4 side working operation transmission line. Thereby, the communication of data signals is secured by by-passing the failed transmission line.
Recovery operation performed when both working operation and stand-by transmission lines experiences a failure between the node 2 and node 3 is shown in FIG. 17(c). In this case, in the node 2, the cross connector section changes connection from the path that a data signal is allowed to be communicated through the operation transmission line side between the node 2 and node 3 for insertion division, to the path that a data signal is allowed to be communicated through the stand-by transmission side between the node 2 and node 1 for insertion division. On the other hand, in the node 3, the cross connector section performs path change so that an optical signal inputted/outputted through the node 4 side stand-by transmission line is connected to an optical signal inputted/outputted through the node 4 side operation transmission line. Thereby, the communication of data signals is secured by by-passing the failed transmission line.
Recovery operation performed when the node 3 experiences a failure is shown in FIG. 17(d). In this case, in the node 2, the cross connector section changes connection from the path that a data signal is allowed to be communicated through the operation transmission line side between the node 2 and node 3 for insertion division, to the path that a data signal is allowed to be communicated through the stand-by transmission side between the node 2 and node 1 for insertion division. On the other hand, in the node 4, the cross connector section performs path change so that an optical signal inputted/outputted through the node 5 side stand-by transmission line is connected to an optical signal inputted/outputted through the node 5 side operation transmission line. Thereby, the communication of data signals is secured by by-passing the node that has failed.
Next, another conventional ring optical transmission device is described. FIG. 18 shows an exemplary structure of a ring optical transmission device comprising m nodes, and each node performs optical division multiplexing of wavelengths of .lambda.1 to .lambda.n and transmits signals.
In FIG. 18, 901-1 to 901-m represent optical insertion division nodes, 902-1 to 902-4 represent transmission line optical fibers (902-1: counter-clockwise working operation system, 902-2: clockwise working operation system, 902-3: clockwise stand-by system, and 902-4: counter-clockwise stand-by system), 1001 represents an optical pre-amplifier, 1002 represents a wavelength division section, 1003 represents a wavelength multiplexing section, 1004 represents an optical booster amplifier, 1005 represents an optical pre-amplifier, 1006 represents a wavelength division section, 1007 represents a wavelength multiplexing section, 1008 represents an optical booster amplifier, 1009-1 to 1009-n represent insertion division devices (ADM), 1010 and 1011 represent optical junction amplifiers, 1012 to 1015 represent 2.times.2 optical switches, 1051 and 1054 represent high speed signal reception interface sections, 1052 and 1053 represent high speed signal transmission interface sections, and 1055 and 1056 represent cross connector sections.
In FIG. 18, m nodes are connected to form a ring with a total four transmission line optical fibers, where two of the lines comprises a first two-way operation system, and where the other two of the lines comprise a second two-way operation system. Each node sends out an optical signal with n wavelengths of .lambda.1 to .lambda.n that are subjected to wavelength division multiplexing to the above-mentioned optical fiber transmission line, and each node receives the optical signal with n wavelengths of .lambda.1 to .lambda.n that are subjected to wavelength division multiplexing from the above-mentioned optical fiber transmission line.
Operation performed during a working (or normal) condition, namely, while there is no failure in the network, is described herein under.
The optical signal received from the counter-clockwise operation transmission line optical fiber is amplified by the optical pre-amplifier 1001 through the 2.times.2 optical switch 1012, and divided into n wavelength components having wavelengths of .lambda.1 to .lambda.n by the wavelength division section. The wavelength divided n optical signals having wavelengths of .lambda.1 to .lambda.n are inputted to the ADM devices 1009-1 to 1009-n. In detail, the optical signal having a wavelength of .lambda.1 is inputted to the ADM device 1009-1, the optical signal having a wavelength of .lambda.2 is inputted to the ADM device 1009-2, and the optical signal having a wavelength of .lambda.n is inputted to the ADM device 1009-n.
n optical signals having wavelengths of .lambda.1 to .lambda.n are outputted from the respective ADM devices 1009-1 to 1009-n. In detail, the optical signal having the wavelength of .lambda.1 is outputted from the ADM device 1009-1, the optical signal having the wavelength of .lambda.2 is outputted from the ADM device 1009-2, and the optical signal having the wavelength of .lambda.n is outputted from the ADM device 1009-n. n optical signals having wavelengths of .lambda.1 to .lambda.n outputted from the respective ADM devices 1009-1 to 1009-n are subjected to wavelength division multiplexing in the wavelength multiplexing section 1003 for forming a signal optical signal and the single optical signal is amplified by the optical booster amplifier 1004, and sent out to the counter-clockwise operation optical fiber transmission line through the 2.times.2 optical switch 1013. The optical signal transmitted/received through the clockwise operation system 902-2 is subjected to multiplexing division operation in the same way as described herein above.
In FIG. 18, the 2.times.2 optical switch 1015, optical pre-amplifier 1005, wavelength division section 1006, wavelength multiplexing section 1007, optical booster amplifier 1008, and 2.times.2 optical switch 1014 are applied to the clockwise operation system.
Next, recovery operation performed when the transmission line of the conventional ring optical transmission device shown in FIG. 18 experiences a failure is described herein under. FIG. 19 is a set of diagrams for illustrating the recovery operation.
In FIG. 19(a) during working operation, data signals are communicated between the node 2 and the node 5 through a first two-way working operation transmission system that includes two lines. The node 2 and node 5 output/input data signals through the low speed signal interface section in the respective nodes, and cross connector sections set the path.
Recovery operation performed when two working operation transmission lines experiences a failure between the node 2 and node 3 is shown in FIG. 19(b). In this case, in the node 2, the 2.times.2 optical switch changes connection from the path that the optical signal is allowed to be communicated through the working operation transmission line side between the node 2 and node 3, to the path that the optical signal is allowed to be communicated through the opposite stand-by transmission side between the node 3 and node 4. Thereby, data signal communication is secured by by-passing the failed transmission line.
Recovery operation performed when both operation and stand-by transmission lines experiences a failure between the node 2 and node 3 is shown in FIG. 19(c). In this case, the data signal communication is secured by by-passing the failed transmission line by way of applying the same operation as described in FIG. 19(b).
Recovery operation performed when the node 3 experiences a failure is shown in FIG. 19(d). In this case, in the node 2, the 2.times.2 optical switch changes connections from the path that the optical signal is allowed to be communicated through the working operation transmission line side between the node 2 and node 3, to the path that the optical signal is allowed to be communicated through the opposite stand-by transmission side between the node 4 and node 5. Thereby, the data signal communication is secured by by-passing the failed transmission line.
The conventional optical transmission device having a ring structure involves problems as described hereinafter.
First, a conventional optical transmission device having a ring structure according to the first conventional art requires four high speed transmission/reception interface sections per one insertion division device (ADM) for performing data signal processing of one wavelength in each node, and a cross connector circuit for performing path change of all the signals connected to these high speed transmission/reception interfaces. Therefore, an optical transmission device having a ring structure involving n wavelengths should have n times devices, and such an optical transmission device is very expensive and large-sized, thereby causing a problem.
Next, a conventional optical transmission device having a ring structure according to the second conventional art can set the optical signal outputted from each node to only two paths of the working operation transmission line and opposite stand-by transmission line, and can not change the path to the stand-by transmission line in the same direction. As shown in FIG. 19, when the operation transmission line between the node 2 and node 3 fails and the node 6 fails simultaneously, the node 2 can not communicate with the node 5 in the case of the second conventional art. Therefore, an optical transmission device having a ring structure of this type is disadvantageous in that the reliability in failure measure is low, and thereby causing a problem.